1. Field of the Invention
This invention relates generally to a system for rejecting heat in a lunar environment and more particularly to a passive device for rejecting habitat waste heat at a location on or near the lunar equator utilizing a reflective flexible structure which is in a compact form for space travel and which can be deployed on the lunar surface.
2. Background Art
For aerospace applications, thermal or heat management is crucial to life support. The purpose of this invention is to provide a means of dissipating waste heat under certain limited conditions on the lunar surface.
In a lunar system, it is expected that the thermal environment at the lunar equator, and at latitudes up to about 50.degree., will require a system to decrease the ambient heat sink temperature or increase the waste heat temperature in order to increase the thermal operating efficiency of thermal control systems In the vacuum of space, such a system must reject by thermal radiation the waste heat collected from a crew and from electrical equipment.
Because of the space environment, the surface temperature near the lunar equator ranges from 102.degree. K. at night to a peak of 384.degree. K. during the day. With this hot lunar environment, dissipation or heat rejection of thermal radiation becomes a problem when the heat sink temperature exceeds the temperature of the heat to be dissipated. "Heat sink temperature" is the temperature to which the heat can be transferred by radiation, and must be less than the source temperature. As the heat sink temperature is reduced more and more below the source temperature, the efficiency of heat transfer increases. In a lunar environment, the heat sink temperature at solar noon for a typical vertical unshaded radiator at the equator is 322.degree. K.
There are basically two ways this problem of the hot lunar environment can be solved. One way is to use an electrically or thermally powered heat pump to elevate the heat source temperature. Alternately a thermal radiation shading device can be employed to shield the radiator from the hot environment. Since heat pumps require a great deal of electrical or thermal energy to operate, a passive radiator shade device is desirable to shield the radiator from the hot environment and to reduce the effective heat sink temperature of the radiator. Radiator shade devices require little or no power and have no working parts once set up. However, they are typically large and cumbersome to set up.
Pertinent Prior Art includes the following:
U.S. Pat. No. 3,310,102 to Trombe.
U.S. Pat. No. 4,624,113 to Hull et al.
U.S. Pat. No. 4,624,113 to Hull et al. disclosed a radiative cooling system having a radiating surface aimed at the sky by a housing of compound parabolic aluminum mirrors. The radiating surface is surrounded by a transparent cover which is thermally isolated from the radiating surface by a vacuum.
U.S. Pat. No. 3,310,102 to Trombe discloses a radiator cooling system having an infrared radiating body, an opaque envelope surrounding the radiator (for thermally insulating the radiator), and a reflective lining (such as non-oxidized aluminum which reflects 99% of infrared radiation) disposed within the envelope. The reflective lining is shaped to reflect the radiations emitted by the radiator into space. In one embodiment, the reflective lining has a cylindroparabolic shape. The exterior of the envelope is coated with a substance capable of reflecting sun rays.